Marking the std::mt19937 *gen argument in `runtime/include/QuantumD…

…evice.hpp/SetDevicePRNG(std::mt19937 *gen)` as `[[maybe_unused]]`, as some devices (e.g. openqasm and oqc) do not support seeding has this argument has no effect in the default implementation of this setter.

At a more superficial level, this is to make the tests in PennyLaneAI/pennylane-lightning#819 pass.

runtime/include/QuantumDevice.hpp

@@ -122,7 +122,7 @@ struct QuantumDevice {
      *
      * @param gen The std::mt19937 PRNG object.
      */
-    virtual void SetDevicePRNG(std::mt19937 *gen){};
+    virtual void SetDevicePRNG([[maybe_unused]] std::mt19937 *gen){};
 
     /**
      * @brief Start recording a quantum tape if provided.